I have a Bosch dizzy on my Speedster. I think they have a Pertronix part to change it to electronic ignition. The car has no starter or coils, and is still 6V.
Is it worth the cost? Has anyone else upgraded their dizzy?
They recommend a 3 ohm 40,000 volt coil. Would just changing to a new coil make much of a difference with the current distributor setup?
Thank you for your input.
I doubt you would notice a difference, other than possible improved reliability. I've been running one for years on the Fronty with 12v.
My old Allen disturbutor machine shows the timing to be rock steady with the Pert, and a few degrees wobbly with points. The wobbly no doubt is from a worn shaft/bushing.
When I bought the rebuilt 300 I6 for my f100, it had the pertronix in it.I didnt trust it and I put the points in the glove box.I aint had to change yet and that has been 10 years now.It does seem to be reliable.I dont recall the need for a better than stock coil though as I am running a stock coil best I can remember.
The Pertronics makes the distributor work as well as it would with a properly adjusted set of points. Is it worth $125 for you to avoid replacing the points every 10,000 miles?
The Pertronics coil at 3 ohms will pull 4 Amps all the time. If you have a stock Model T generator that is nearly half the available output. You won't be able to use headlights while the engine is running.
I run 12 volts and the Pertronics got fried when the new replacement three way regulator spiked up to 18 volts. I changed back to points and it will not idle as slow as it does with the Pertronics though.
Where do you get those numbers, Royce?
They are impossible, as the coil can't fire until the circuit opens. The Pert itself draws insignificant current. The power going into a coil is dwell percentage times coil primary current, or about half of primary current.
Small point gap, burned points, wet points, week condenser, too many connections and what ever else can be trouble along the way.
The Petronics is the way to go. There are just two connections to make, one on each terminal of the coil.
No need to use a high output coil.
Just use the standard coils as they will put out all the spark you need.
I would stay away from the Petronics coils.
They draw too much juice and have a reputation for suddenly dropping dead after a few hours of use.
If you are running on 6 volts just order a $7 '66 VW coil from your favorite online parts house or for a '67 VW if you have 12 volts.
You can order the Petronics dist. module from your local NAPA type parts store.
Dave, there is one feature of electronic ignition no one mentioned. When it fails there will be no warning, no rough running engine, it will just be dead. You cannot fix the electronic ignition along side the road unless you have a spare system or a set of points and condenser with which to replace the Petronix. There is a lot to be said for using breaker points. A high voltage coil would be nice but an ordinary coil will work just fine. This is a Model T remember.
Ralph,
I=R/E is one of the equations that makes up Ohm's Law. It is just like California law except it is fair and makes sense.
Current (I) is a direct result of the resistance (R) and the voltage (E) in the circuit. It is really simple.
So if for example the resistance (R) was 1 ohm the current (I) would be 12 amps when using a 12 volt power source.
Royce, but you failed in your first post.
Dave is using 6 v., and he listed a 3 ohm coil. hence 6v/3ohm = 2A.
2A at 50% dwell is 1A average, which is what counts in this job.
Just like points, the Pert draws insignificant current when the coil primary circuit is open. For a low rpm engine, Pert could build a magnet with shorter duration in front of the pickup, and shorten dwell time by at least half again, and reduce average current proportionally.
The early Atwater-Kent disturbutors had snap action points, which were closed only briefly. They claimed up to 2,000 miles on a set of dry cells.
If you want to redce average current with points, open them up to reduce dwell. Lots of dwell time is needed at high rpm only.
Oh, I overlooked one thing in your last post, Royce:
I = E/R
not how you have it.
Geez, he even distorts proven laws of physics ?
Anyway, a consequence of shortening the dwell time will reduce primary current and hence the amount of energy stored in the primary winding. That means less spark energy which could adversely impact ignition and overall engine performance.
Ralph,
The Pertronics coil only comes in 12 volts. The information I provided is thus accurate.
As you know, Mike, the dwell time has to be only long enough to saturate the coil. After that, it's waste heat. A points-type coil designed for an engine that turns 6,000 rpm, such as a Porsche 914 (source of my dist and coil) has to saturate in one third the time that it gets current at 2,000 rpm. Hence, 2/3 of the current into the coil at 2,000 rpm is waste.
You can put the same coil on a T with 2,000 rpm redline, and it will work as good with 15 degrees dwell as it would with 45 degrees dwell (50%), and will draw one-third the current. Thus, with a 3 ohm coil, current draw at 12 volts will not be 4 amps, but 0.7 amps.
I thought only Lucas tried to repeal Ohm's Law...
rdr
So when you get a Petronix for a 6 volt system you MUST use a good coil, not a Petronix.
I often wonder how a company that can make and sell such a fine elecronic conversion system can sell a poor coil and not even have a coil for a 6 voly unit.
I bet that 3 ohm 40KV coil would work fine at 6V on a normal or even high compression T. 20KV should be plenty at .030 gap.
Ralph, I see your point. The coil current must reach a minimum value to store enough energy, which when efficiently transferred to the secondary winding, produces a spark with sufficient energy level to guarantee reliable ignition over a wide range of combustion variables. Ensuring the coil dwell is long enough at 2,000 RPM will definitely mean longer dwell, higher peak current and excess energy stored at lower RPM
The coil current charges nearly linearly due to the coil inductance assuming you do NOT saturate the core and can be calculated with the formula: Ipri = (Vpri * t)/L where t is the dwell time and L is the inductance of the coil in Henrys. You can calculate the coil current and associated dwell time necessary to charge the coil to the same energy level as a standard Model T coil if you know the coil inductance. A typical 3.3mH Model T coil operating from 6V dwells for approximately 3ms so the peak current I = (V*t)/L = 6 * 0.0035/0.0033 = 5.45A The energy stored in the primary can be calculated by: Epri = 1/2 * L * I^2 = 1/2 * 0.0033 * (5.45)^2 = 0.049J
The selection guide on the Pertronix website: http://www.pertronix.com/catalogs/pdf/ptx/2010/ptx2010_coils.pdf does in fact list coils intended for 6V operation; P/N: 40011 40,000 Volt coil for 4 cylinder cars operating from 6V. That coil specification is: Lpri=6.4mH and so to store the same energy in the primary winding of that coil as a typical Model T coil requires a peak current of: Ipri = Sqrt(Epri *2)/L = Sqrt(0.049*2/0.0064) = 3.91A The dwell time required to achieve that level of peak current is: t = (L*I)/V = 0.0064 * 3.91 / 6 = 0.00416s = 4.16ms. Note that the current is the peak value at the time the points open NOT the average current. The primary current charges nearly linearly during the 4.16ms dwell time so the average value is 3.9/2 * Duty Cycle. At 2000 RPM, 4.16ms dwell time represents a dwell angle of 50 deg so the duty cycle is 50/360 = 13.9% so the average current would be: (3.9/2) * 0.139 = 0.271A * 4 cylinders = 1.08A. Ralph’s point, dwelling for 50deg to support higher engine RPM operation is just storing more energy than necessary and wasting power. At 500 RPM idle, a dwell angle of 50 degrees corresponds to a dwell time of 0.0167s for which the coil peak current would reach: I = V*t/L = 6 * 0.0167/0.0064 = 15.6A if it were not for the DC winding resistance, which is 1.5 Ohms for the specified coil. That limits the current to I = E/R = 6/1.5 = 4A so the average current will be 4/2 * 0.139 = 0.278A * 4 cylinders = 1.112A so the average coil current will remain nearly the same.
An Electronic ignition provide the benefit of greater efficiency by maintaining the minimum coil dwell time regardless of engine RPM so that the same spark energy is always available without raising the average coil current as the engine RPM drops and wasting power.
At 500 RPM, maintaining a 4.16ms ensures the same spark energy but this dwell time represents a dwell angle of only 12.5 deg so the duty cycle is 12.5/360 = 3.5% so the average current would be: (3.9/2) * 0.035 = 0.0683A * 4 cylinders = 0.273A using an electronic ignition module. This is precisely how a popular Model T electronic ignition functions :-)
You been doin' your homework, Mike. I've never checked dwell percentage on a Pert, so don't know if it changes dwell with rpm. I highly doubt it.
Your E-Timer keeping constant dwell time instead of constant dwell percentage means less current draw and less heating of the poor old buzz coils at all rpm less than max. Good deed, indeed.
The 914 mentioned above with points is set to about 45 degrees dwell, or about 50% dwell time, all the time. That's 0.016" gap.
I must say, your compacted paragraphs combined with limited text features here make your posts a bit hard to read. Maybe you could make circular charts showing dwell for a disturbutor, your E-Timer, and buzz coils on both battery and mag?
rdr
Easier on the buzz coils absolutely but another key benefit of the constant dwell of the Electronic Ignition is significantly longer battery life.
The benefit is actually more than I stated previously due to an error in calculating the current; its not 4/2A. At 500 RPM, the coil current with fixed dwell of 50 deg would ramp up linearly for the first 4.3ms then saturate at 6/1.5 = 4A for the remaining 12.5ms of the dwell time for an average current of: 3.5A * 0.139 = 0.485A * 4 cylinders = 1.94A Thus, Electronic Ignition would only draw about 14% of the current of the constant 50 deg dwell angle ignition.
What's old is new, again, again. See, Mike, you didn't make a real breakthough. The 1911 Atwater-Kent Uni-sparker snap action points disturbutor does the same job: constant dwell, regardless of rpm. I should try to find one of those to play with.
I don't know now where I saw a Uni-sparker with the cap off, but the rotor ramps up to where the points suddenly make contact, then release immediately. I also have no idea of the RPM limit or durability of that set of points.
---------
Is it too late to introduce a definition of DWELL? Dwell is the amount of time the points on a points-type disturbutor are closed, causing current to flow through the primary of a High Tension coil. As above, it is expressed in percentage, degrees, or time.
rdr
Of course the Ford magneto draws zero battery current and is more reliable than any electronic device.
Yeh, Royce, and it's easily maintainable, too.
Unfortunately my Speedster does not have a magneto. All that was removed to reduce weight in the engine and allow the car to go faster.
Just a distributor and a generator. I assume the only purpose of the battery is to help with starting and to store the excess energy produced by the generator that is not used while the car is running.
Nice chunk of information that Mike presented earlier.
Mike
Can you come up with an e-distributor that works as well as you e-timer?
Dave,
Thanks for your comments. One of the reasons I took on the E-Timer project was the challenge of getting it to work within the confines of the original ignition footprint and wiring while retaining the sound and appearance of stock operation. Superior engine performance, greater efficiency and automatic timing advance were stretch goals added once the fundamental challenge of getting it all to fit and operate without altering the original wiring was achieved.
I thought there were several distributor options available for the Model T including versions with electronic pick-ups and ignition control. Also, no need to preserve stock appearance permits many more options to improve performance. That’s why I really did not give that much thought. Still interesting to ponder the technical merits and challenges of distributor operation applied to a Model T though.
If you have a good alternator I would recommend using an MSD 6AL box. It is compatible with the breaker points in your distributor and will put out enough power to weld with. And way cheaper than an E timer too!
The MSD 6AL is a capacitive discharge type unit. The points become a trigger only, not the path of the current to the coil. So you can run a very low resistance / high output coil. And the points won't ever wear out. Spark plugs will never foul no matter how far off the mixture might be. This type of ignition will support perhaps 1000 horsepower. Surely that will be sufficient for your needs?
Link:
http://www.summitracing.com/parts/MSD-6425/